The magnesium deficiency syndrome is most severe in the youngest mammals; they may develop apnea and bradycardia. We are reviewing records of St. Louis neonates with these findings; some infants were diagnosed as magnestium deficient and treated with magnesium. We will explore the feasibility of conducting a properly controlled study in neonates. We are exploring the congentital magnesium deficiency syndrome, studying the concentration of magnesium and other cations in tissues of young rate pups born to dams fed 5 to 150 mg of magnesium/100 g purified diet. The kidney of the magnesium deficient mammal avidly retains magnesium. We are studying the effect of parenteral furosemide in weanling and young adult rats fed several levels of dietary magnesium. The physical state and the renal excretion and tissue levels of several cations will be examined. Although weanling rats suffered no ill effect, rat dams fed 150 mg of magnesium as laboratory grade MgCO3 suffered high fetal wastage. We will compare this with a) dams fed certified MgCO3 and b) dams fed dolomite, which is CaMg(cO3)2, marketed in an unrefined state for human consumption. We are studying cardiopulmonary histopathology in acute Mg deficiency.